This application is based on Japanese Patent Application No. 2000-402219 filed on Dec. 28, 2000, No. 2000-402220 filed on Dec. 28, 2000, and No. 2001-246366 filed on Aug. 15, 2001, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a braking system.
2. Discussion of Related Art
JP-A-9-511967 discloses a braking system including (a) brake cylinder arranged to operate a brake with a hydraulic pressure, (b) a master cylinder including a pressurizing piston which is operated according to an operation of a manually operable brake operating member, to pressurize a working fluid in a pressurizing chamber formed in front of the pressurizing piston, (c) a high-pressure source in the form of a pressure-control cylinder including a control piston operated according to an operation of an electric motor, and having a control pressure chamber which is formed in front of the control piton and which is connected to the brake cylinder, and (d) a braking-pressure control device operable to control an electric energy to be supplied to the electric motor, for controlling a pressure of the fluid in the control pressure chamber of the pressure control cylinder, to thereby control the fluid pressure in the brake cylinder.
It is therefore an object of the present invention to provide a braking system which provides improvements over a known braking system as disclosed in the above-identified publication, for instance, improved efficiency of utilization of the electric energy and/or reduction of a required amount of consumption of the electric energy in various manners.
The above object may be achieved by a braking system constructed according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate and clarify possible combinations of elements or technical features. It is to be understood that the present invention is not limited to the technical features or any combinations thereof which will be described for illustrative purpose only. It is to be further understood that a plurality of elements or features included in any one of the following modes of the invention are not necessarily provided all together, and that the invention may be embodied without some of the elements or features described with respect to the same mode.
(1) A braking system comprising: (a) a hydraulically operated brake cylinder for operating a brake, (b) a master cylinder operable according to an operation of a manually operable brake operating member, to pressurize a working fluid, (c) a master-cylinder cut-off valve connected to the master cylinder, (d) a high-pressure source disposed between the master-cylinder cut-off valve and the brake cylinder and operable according to the operation of the brake operating member, to pressurize the fluid, the high-pressure source including a power-operated drive device and a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front control-pressure chamber being connected to the brake cylinder while the rear pressure chamber being held in communication with the master cylinder, and (e) a braking-pressure control device operable to control the power-operated drive device, to thereby control the pressure of the fluid in the brake cylinder.
In the braking system according to the above mode (1) of the present invention, the brake cylinder can be operated with not only the pressure of the fluid pressurized by the high-pressure source, but also the pressure of the fluid which is pressurized by the master cylinder. In other words, the pressurized fluid delivered from the master cylinder can be utilized, in addition to the pressurized fluid delivered from the high-pressure source, to operate the brake cylinder. Accordingly, the high-pressure source can be economically operated with a comparatively small amount of electric energy, and the brake cylinder can be operated to produce a relatively high braking effect. The fluid pressure in the brake cylinder is controlled by the pressure-control cylinder operated by the power-operated drive device under the control of the braking-pressure control device. Further, the rear pressure chamber is connected to the master cylinder such that the rear pressure chamber is normally held in communication with the master cylinder, so that the fluid pressurized by the master cylinder can be utilized to control the fluid pressure in the brake cylinder. In a conventional braking system wherein the fluid pressure in the brake cylinder is controlled by the pressure-control cylinder, the master cylinder is communicated with a stroke simulator but is not utilized to control the fluid pressure in the brake cylinder. In the braking system according to the above mode (1), on the other hand, the pressurized fluid delivered from the master cylinder is used to control the brake cylinder pressure, so that the drive force required to be produced by the power-operated drive device to operate the control piston of the pressure-control cylinder is accordingly reduced
(2) A braking system comprising: (a) a hydraulically operated brake cylinder for operating a brake, (b) a master cylinder operable according to an operation of a manually operable brake operating member, to pressurize a working fluid, (c) a master-cylinder cut-off valve connected to the master cylinder, (d) a high-pressure source disposed between the master-cylinder cut-off valve and the brake cylinder and operable according to the operation of the brake operating member, to pressurize the fluid, the high-pressure source including a power-operated drive device and a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front control-pressure chamber being connected to the brake cylinder while the rear pressure chamber being normally held in communication with the master cylinder, and (e) a braking-pressure control device operable to control the power-operated drive device, to thereby control the pressure of the fluid in the brake cylinder.
The braking system according to the above mode (2) has substantially the same advantage as the braking system according to the above mode (1).
(3) A braking system according to the above mode (2), further comprising a fluid passage connecting the master cylinder and the control-pressure chamber, and wherein the master-cylinder cut-off valve is disposed in the fluid passage, and has an open state in which the master cylinder and the control-pressure chamber are communicated with each other, and a closed state in which the master cylinder and the control-pressure chamber are isolated from each other.
In the braking system according to the above mode (3), the master-cylinder cut-off valve is disposed in the fluid passage connecting the master cylinder and the control-pressure chamber of the pressure-control cylinder. When the master-cylinder cut-off valve is placed in the open state, the master cylinder is communicated with the brake cylinder through the cut-off valve, so that the pressurized fluid delivered from the master cylinder is supplied to the brake cylinder, to operate the brake. When the master-cylinder cut-off valve is placed in the closed state, the control-pressure chamber is isolated from the master cylinder, and the fluid pressurized in the control-pressure chamber is delivered to the brake cylinder, to operate the brake.
(4) A braking system according to the above mode (2) o (3), wherein the braking-pressure control device includes an operation detecting portion operable to detect an operating state of the brake operating member, the braking-pressure control device controlling the power-operated drive device on the basis of the operating state detected by the operation detecting portion.
In the braking system according to the above mode (4), the power-operated drive device to operate the pressure-control cylinder is controlled on the basis of the detected operating state of the manually operable brake operating member.
The operation detecting portion may detect the operating state of the brake operating member, on the basis of an output signal of an operation detector or sensor, such as a sensor for detecting an operating amount of the brake operating member, such as an operating force or stroke, or a sensor for detecting a physical quantity corresponding to the operating amount of the brake operating member, such as the fluid pressure in the master cylinder, or any other fluid pressure equivalent to the master cylinder pressure. The physical quantity may be a deceleration value of an automotive vehicle which is equipped with the present braking system. The power-operated drive device, which is controlled on the basis of the detected operating state of the brake operating member, may be controlled according to the detected operating state of the brake operating member, or a state of change of the detected operating state.
(5) A braking system according to any one of the above modes (2)-(4), wherein the braking-pressure control device controls the power-operated drive device such that the pressure of the fluid in the control-pressure chamber is controlled to a level determined by the detected operating state of the brake operating member.
In the braking system according to the above mode (5), the fluid pressure in the control-pressure chamber is controlled to the level corresponding to the detected operating state of the brake operating member, so that the fluid pressure in the brake cylinder is controlled to that level.
(6) A braking system according to any one of the above modes (2)-(5), which is arranged such that a volume of the rear pressure chamber is changed as the manually operated brake operating member is operated, while the power-operated drive device is controlled to operate the control piston of the pressure-control cylinder.
(7) A braking system according to any one of the above modes (2)-(7), which is arranged such that the pressure of the fluid in the rear pressure chamber is controlled to a level corresponding to an operating force of the manually operable brake operating member, while the power-operated drive device is controlled to operate the control piston of the pressure-control cylinder.
Since the rear pressure chamber is communicated with the master cylinder, the fluid can flow between the rear pressure chamber and the master cylinder. Where the braking system is arranged such that the volume of the rear pressure chamber is changed as the brake operating member is operated and such that the fluid pressure in the rear pressure chamber is controlled to the level corresponding to the operating force of the brake operating member, the brake operating member may be given a reaction force corresponding to its operating force. In this case, the pressure-control cylinder is considered to function as a stroke simulator, and therefore the braking system does not require an exclusive stroke simulator.
(8) A braking system according to any one of the above modes (3)-(7), wherein the master-cylinder cut-off valve is an electromagnetic shut-off valve which is switched at least between the open and closed state depending upon an amount of electric current applied thereto, and the braking-pressure control device controls the power-operated drive device to control the fluid pressure in the brake cylinder, while the electromagnetic shut-off valve is placed in the closed state.
In the braking system according to the above mode (8), the fluid pressure in the control-pressure chamber is controlled while the control-pressure chamber of the pressure-control cylinder is isolated or disconnected from the master cylinder.
(9) A braking system according to any one of the above modes (2)-(8), wherein the control piston of the pressure-control cylinder has a rear pressure-receiving surface partially defining the rear pressure chamber and a rear pressure-receiving surface partially defining the control-pressure chamber, the pressure-receiving surface having a smaller area than the front pressure-receiving surface.
In the braking system according to the above mode (9) wherein the area of the rear pressure-receiving surface partially defining the rear pressure chamber of the pressure-control cylinder is made smaller than that of the front pressure-receiving surface partially defining the control-pressure chamber, the amount of the fluid supplied from the master cylinder to the rear pressure chamber is made smaller than the amount of the fluid delivered from the control-pressure chamber to the brake cylinder. This arrangement is effective to reduce an increase in the amount of the pressurized fluid required to be delivered to the rear pressure chamber of the pressure-control cylinder, so that the required operating stroke of the brake operating member to provide a given braking effect can be reduced. Since the required operating stroke can be reduced while the maser cylinder is isolated from the brake cylinder, the master cylinder need not be connected to a stroke simulator, because the pressure-control cylinder achieves substantially the same function as a stroke simulator connected to the master cylinder.
(10) A braking system according to any one of the above modes (2)-(9), wherein the master cylinder includes a pressurizing piston which is connected to the manually operable brake operating member and which includes a rear large-diameter portion on the side of the brake operating member, and a front small-diameter portion partially defining a pressurizing chamber in front of the small-diameter portion, the front small-diameter portion having a smaller diameter than the rear large-diameter portion, and wherein the pressurizing chamber of the master cylinder is connected to the rear pressure chamber of the pressure-control cylinder.
In the master cylinder of the braking system according to the above mode (10), the pressurizing chamber is partially defined by the front small-diameter portion of the pressurizing piston, which has a smaller diameter than the rear large-diameter portion on the side of the brake operating member. Accordingly, the fluid pressure in the pressurizing chamber when the brake operating member is operated at a given operating force can be made higher than in a master cylinder in which the pressurizing piston does not have the small-diameter and large-diameter portions. Thus, the present arrangement permits a relatively higher fluid pressure in the pressurizing chamber for a given operating force of the brake operating member, that is, a relatively high boosting ratio of the brake operating force.
The fluid pressure in the brake cylinder while the brake cylinder is communicated with the master cylinder can be made comparatively high for a give operating force of the brake operating member, so that the reduction of the fluid pressure in the brake cylinder while the pressure-control cylinder is not in operation.
(11) A braking system characterized comprising:
a hydraulically operated brake cylinder for operating a brake;
a master cylinder operable according to an operation of a manually operable brake operating member, to pressurize a working fluid;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front control-pressure chamber being connected to the brake cylinder while the rear pressure chamber being directly connected through a fluid passage to the master cylinder; and
a braking-pressure control device operable to control the power-operated drive device, to thereby control the pressure of the fluid in the brake cylinder.
In the braking system according to the above mode (11) wherein the master cylinder and the rear pressure chamber of the pressure-control cylinder are directly communicated with each other through a fluid passage which is not provided with any valve or stroke simulator.
The technical feature according to any one of the above modes (1)-(10) is applicable to the braking system according to the above mode (11).
(12) A braking system according to the above mode (1), wherein the master cylinder includes a pressurizing piston which partially defines a pressurizing chamber and which is operable by the manually operable brake operating member, to pressurize the fluid in the pressurizing chamber, and the high-pressure source comprises a power-operated drive device, and a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front control-pressure chamber being connected to the brake cylinder, while the rear pressure chamber being connected to the pressurizing chamber such that a pressure of the fluid pressurized in the pressurizing chamber is applicable to the rear pressure chamber, the braking system further comprising a braking-pressure control device operable to control an electric energy to be applied to the power-operated drive device, for controlling the pressure of the fluid in the front control-pressure chamber, to thereby control the pressure of the fluid in the brake cylinder.
In the braking system according to the above mode (12) of this invention, the supply or application of an electric energy or power to the power-operated drive device is controlled to control a drive force which acts on the control piston of the pressure-control cylinder. As a result, the pressure of the fluid in the control-pressure chamber formed in front of the control piston is controlled to control the pressure of the fluid in the brake cylinder. During this control of the power-operated drive device, the fluid pressurized in the pressurizing chamber of the master cylinder is delivered to the rear pressure chamber of the pressure-control cylinder. Thus, the pressurized fluid delivered from the pressurizing chamber of the master cylinder is utilized by the pressure-control cylinder to control the fluid pressure in the brake cylinder. Accordingly, the required amount of electric energy to operate the power-operated drive device can be reduced.
In a braking system equipped with a pressure-control cylinder operated according to an operation of a power-operated drive device, the fluid pressure in the brake cylinder is usually controlled while the brake cylinder is isolated from the master cylinder. In the conventional braking system of this type, the fluid pressurized by the master cylinder is not utilized to control the fluid pressure in the brake cylinder. In the braking system according to the above mode (12), the pressurized fluid delivered from the master cylinder is utilized to control the fluid pressure in the brake cylinder.
For instance, the fluid pressurized by the master cylinder is delivered to the rear pressure chamber of the pressure-control cylinder, to increase the fluid pressure in the rear pressure chamber, for thereby assisting the power-operated drive device to drive the control piston. Where the fluid pressure in the brake cylinder cannot be controlled by the pressure-control cylinder due to a failure or defect of the power-operated drive device, the pressurized fluid may be delivered from the master cylinder to the rear pressure chamber of the pressure-control cylinder, so that the control piston is advanced with a force based on the fluid pressure in the rear pressure chamber, to thereby increase the fluid pressure in the control-pressure chamber. Conventionally, the pressurized fluid discharged from the master cylinder while the master cylinder is disconnected from the brake cylinder is absorbed or accommodated in a stroke simulator, but is not utilized to increase the fluid pressure in the brake cylinder. According to the above mode (12) of this invention, however, the pressurized fluid in the master cylinder is effectively used to control the brake cylinder pressure. Further, the reduction of the brake cylinder pressure due to a discharge flow of the pressurized fluid from the rear pressure chamber can be reduced by providing suitable means for restricting or inhibiting the discharge flow of the fluid from the rear pressure chamber.
The pressurized fluid may be delivered from the pressurizing chamber of the master cylinder either directly or indirectly to the rear pressure chamber of the pressure-control cylinder. For instance, the indirect delivery may be achieved via a stroke simulator disposed in a fluid passage connecting the pressurizing chamber and the rear pressure chamber, as described below. In this case, the pressurized fluid is delivered to one of two variable-volume chambers of the stroke simulator, so that the volume of the other variable-volume chamber is reduced to deliver the fluid to the rear pressure chamber. In this case, too, the pressure of the fluid pressurized in the pressurizing chamber of the master cylinder is substantially applied to the rear pressure chamber through the stroke simulator, although the pressure of the pressurized fluid applied to the rear pressure chamber and the rate of flow of the fluid into the rear pressure chamber are not necessarily exactly equal to the fluid pressure in the pressurizing chamber and the rate of delivery of the pressurized fluid from the pressurizing chamber.
The power-operated drive device may includes an operating portion such as an electric motor, and an energy source such as a battery.
(13) A braking system according to the above mode (12), further comprising a stroke simulator including:
a housing;
a simulator piston slidably received within the housing and cooperating with the housing to define a first variable-volume chamber and a second variable-volume chamber, the first variable-volume chamber being connected to the pressurizing chamber of the master cylinder, while the second variable-volume chamber being connected to the rear pressure chamber of the pressure-control cylinder; and
biasing means for biasing the simulator piston in a direction that causes a volume of the first variable-volume chamber to be reduced.
In the braking system according to the above mode (13), the pressurized fluid is delivered from the pressurizing chamber of the master cylinder indirectly to the rear pressure chamber of the pressure-control cylinder through the stroke simulator. When the pressurized fluid is delivered from the master cylinder to the first variable-volume chamber, the fluid is delivered from the second variable-volume chamber to the rear pressure chamber of the pressure-control cylinder.
Where the fluid pressure in the brake cylinder is controlled while the master cylinder is isolated from the brake cylinder, the master cylinder is usually connected to a stroke simulator. In this case, the fluid pressurized in the second variable-volume chamber can be utilized for the pressure-control cylinder.
When the brake operating member is released, the pressurized fluid may be discharged from the rear pressure chamber to the second variable-volume chamber, so that the fluid can be returned from the first variable-volume chamber to the master cylinder.
(14) A braking system according to the above mode (13), which is arranged such that an amount of increase of the volume of the rear pressure chamber is larger than an amount of decrease of the second variable-volume chamber of the stroke simulator.
In the braking system according to the above mode (14), the entire amount of the fluid discharged from the second variable-volume chamber of the stroke simulator can be accommodated in the rear pressure chamber of the pressure-control cylinder. Thus, the fluid in the second variable-volume chamber can be effectively used to operate the control piston. Further, the delivery of the fluid from the second variable-volume chamber into the rear pressure chamber prevents an excessive rise of the fluid pressure in the second variable-volume chamber, thereby avoiding an excessive increase of the reaction force acting on the manually operable brake operating member being depressed by the operator.
(15) A braking system according to any one of the above modes (12)-(14), further comprising:
a low-pressure source which stores the working fluid under a pressure substantially equal to an atmospheric pressure; and
a valve device disposed in a fluid passage connecting the low-pressure source and the rear pressure chamber of the pressure-control cylinder, and operable to control a flow of the fluid between the low-pressure source and the rear pressure chamber.
In the braking system according to the above mode (15), the valve device is disposed between the low-pressure-source and the rear pressure chamber of the pressure-control cylinder.
The valve device may be arranged to permit a flow of the fluid in a direction from the low-pressure source toward the rear pressure chamber when the fluid pressure in the low-pressure source is higher than that in the rear pressure chamber. This arrangement prevents the fluid pressure in the rear pressure chamber from being lowered below the atmospheric level, and is preferably employed in the braking system according to the above mode (14). Alternatively, the valve device may be arranged to permit a flow of the fluid from the low-pressure source to the rear pressure chamber when the amount of increase of the volume of the rear pressure chamber is larger than the amount of decrease of the volume of the second variable-volume chamber of the stroke simulator. This arrangement also prevents the fluid pressure in the rear pressure chamber from being lowered below the atmospheric level. In this case, the fluid passage provided with the valve device may be considered to serve as a passage for supplying the rear pressure chamber with an additional amount of the fluid which supplements the amount delivered from the second variable-volume chamber.
The valve device may also be arranged to prevent a flow of the fluid in a direction from the rear pressure chamber toward the low-pressure source when the fluid pressure in the rear pressure chamber is higher than that in the low-pressure source. This arrangement for preventing the fluid flow from the rear pressure chamber toward the low-pressure source prevents a drop of the fluid pressure in the rear pressure chamber. Further alternatively, the valve device may be operable between an open state for fluid communication between the rear pressure chamber and the low-pressure source, and a closed state for isolation of the rear pressure chamber and the low-pressure source from each other. In this case, the valve device permits a flow of the fluid from the rear pressure chamber back to the low-pressure source, and a supply of the fluid from the low-pressure source to the rear pressure chamber.
The valve device may be a solenoid-operated or electromagnetic control valve operable by application of an electric current to a solenoid coil, or may be a mechanically operated control valve. Where the valve device is an electromagnetic control valve, it may be an electromagnetic shut-off valve which is opened and closed by energization or de-energization of its solenoid coil. Alternatively, the valve device may be an electromagnetic flow control valve the opening of which is controllable depending upon an amount of an electric current applied to its solenoid coil. The electromagnetic control valve may be a normally open valve which is placed in its open state while its solenoid is in a de-energized state, or a normally closed valve which is placed in its open state while its solenoid is in the de-energized state. The mechanically operated control valve may be a check valve, a pressure-relief valve, a pilot-operated shut-off valve, a pressure regulating valve or a flow control valve.
(16) A braking system according to the above mode (15), wherein the valve device includes a check valve which permits a flow of the fluid in a first direction from the low-pressure source toward the rear pressure chamber and inhibits a flow of the fluid in a second direction opposite to the first direction.
The check valve, which permits the fluid flow from the low-pressure source toward the rear pressure chamber but inhibits the fluid flow from the rear pressure chamber toward the low-pressure source, prevents a drop of the fluid pressure in the rear pressure chamber below the atmospheric level. Further, this check valve does not require an electric energy, unlike an electromagnetic control valve described below with respect to the following mode (17).
(17) A braking system according to the above mode (15) or (16), wherein the valve device includes an electromagnetic control valve which is placed in an open state while the control piston is being advanced.
The fluid is supplied from the low-pressure source to the rear pressure chamber through the electromagnetic control valve placed in the open state during the advancing movement of the control piston, so that it is possible to prevent a drop of the fluid pressure in the rear pressure chamber below the atmospheric level.
If the electromagnetic control valve is placed in the open state also during a retracting movement of the control piston, that is, during reduction of the volume of the rear pressure chamber, the fluid can be returned from the rear pressure chamber back to the low-pressure source when the fluid pressure in the brake cylinder is reduced, or when the brake operating member is released. In this case, the rate or amount of reduction of the fluid pressure in the rear pressure chamber can be controlled by controlling the electromagnetic control valve. Accordingly, it is possible to control the rate or amount of reduction of the fluid pressure in the control-pressure chamber of the pressure-control cylinder, that is, the rate or amount of reduction of the fluid pressure in the brake cylinder.
If the electromagnetic control valve is placed in its closed state when it is required to hold the fluid pressure in the brake cylinder, the retracting movement of the control piston is restricted or prevented, as described below, so that the fluid pressure in the control-pressure chamber can be maintained at the present level, without applying an electric energy to the power-operated drive device.
The valve device may include both of the check valve according to the above mode (16) and the electromagnetic control valve according to the above mode (17). In this case, these check valve and electromagnetic valve are preferably disposed in parallel connection with each other.
(18) A braking system according to any one of the above modes (12)-(17), further comprising a flow-restricting device operable to restrict a discharge flow of the fluid from the rear pressure chamber when the fluid pressure in the brake cylinder is required to be held at a present level.
While the flow-restricting device is preferably a flow-inhibiting device operable to inhibit the fluid flow from the rear pressure chamber, the flow-restricting device may be arranged to assure slow reduction of the fluid pressure in the rear pressure chamber, or prevent rapid reduction of the fluid pressure down to the atmospheric level.
(19) A braking system characterized by comprising:
a hydraulically operated brake cylinder for operating a brake;
a master cylinder operable according to an operation of a manually operable brake operating member, to pressurize a working fluid;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front control-pressure chamber being connected to the brake cylinder;
a braking-pressure control device operable to control an electric energy to be applied to the power-operated drive device, for controlling the pressure of the fluid in the front control-pressure chamber, to thereby control the pressure in the brake cylinder, while the brake cylinder is isolated from the master cylinder; and
a flow-restricting device operable to restrict a discharge flow of the fluid from the rear pressure chamber when the fluid pressure in the brake cylinder is required to be held at a present level.
In the braking system according to the above mode (19), the supply or application of electric current to the power-operated drive device is controlled while the brake cylinder is isolated from the master cylinder. Accordingly, a drive force produced by the power-operated drive device and applied to the control piston is controlled to control the fluid pressure in the front control-pressure chamber. While the fluid pressure in the brake cylinder is required to be held at the present level, the discharge flow of the fluid from the rear pressure chamber is restricted to prevent rapid reduction of the fluid pressure in the rear pressure chamber down to the atmospheric level, for thereby restricting a retracting movement of the control piston, to restrict the fluid pressure reduction in the front control-pressure chamber. When the fluid pressure in the front control-pressure chamber is held at the present level, therefore, the power-operated drive device is not required to produce a drive device, or the required drive device can be reduced, so that the required amount of consumption of electric power by the power-operated drive device can be reduced to hold the fluid pressure in the brake cylinder.
Where the power-operated drive device includes an electric motor and a rotary motion of the electric motor is converted by a motion converting device into a linear motion of a ballscrew to move the control piston, for instance, the control piston is retracted after a force based on the fluid pressure in the control-pressure chamber becomes larger than the drive force acting on the control piston during operation of the electric motor. As a result, the fluid pressure in the control-pressure chamber is reduced with the retracting movement of the control piston. In this case, therefore, the electric energy is required to be kept applied to the electric motor, to prevent the retracting movement of the control piston, that is, to hold the fluid pressure in the control-pressure chamber.
In the above mode (19) of the invention, however, the discharge flow of the fluid from the rear pressure chamber is at least restricted by the flow-restricting device, so that the fluid pressure in the rear pressure chamber is increased to a level determined by the fluid pressure in the control-pressure chamber the configuration of the control piston, etc. Accordingly, the retracting movement of the control piston is prevented to prevent a drop of the fluid pressure in the control-pressure chamber. Since the fluid pressure in the rear pressure chamber is necessarily increased to the level resisting the pressure in the control-pressure chamber, without a drive force produced by the power-operated drive device, substantially no drive force is required to be produced by the power-operated drive device to maintain the fluid pressure in the control-pressure chamber, so that the required amount of consumption of electric energy by the power-operated drive device is reduced. Thus, it is not necessary apply an electric energy to the power-operated drive device, for the purpose of holding the fluid pressure in the control-pressure chamber, that is, unless the application of an electric energy to the drive device is required for any other purpose, for instance, for the purpose of preventing an uncontrolled movement of the ballscrew away from the control piston, to thereby prevent a retracting movement of the control piston, where the ballscrew and the control piston are not fixed to each other. To prevent this movement of the ballscrew, a relatively small amount of electric current is required to be applied to the power-operated drive device. The flow-restricting device has a particularly high effect of reducing the required electric power consumption by the drive device, when the braking system is held in the pressure hold mode for a relatively long time, for instance, where the vehicle equipped with the braking system is held stationary for a long time. The flow-restricting device also has an effect of reducing the operating noise and vibration of the braking system due to the operation of the electric motor.
Where the discharge flow of the fluid from the rear pressure chamber is not completely inhibited but is restricted, an abrupt drop of the fluid pressure in the rear pressure chamber down to the atmospheric level can be prevented, to restrict a retracting movement of the control piston, for reducing the amount of reduction of the fluid pressure in the control-pressure chamber. In this case, the power-operated drive device may be required to be operated to produce a relatively small drive force to hold the fluid pressure in the control-pressure chamber, so that the required electric power consumption by the drive device can be made smaller, than in the case where the fluid pressure in the rear pressure chamber is rapidly lowered to the atmospheric level.
As described above, the flow-restricting device is provided to prevent a rapid drop of the fluid pressure in the rear pressure chamber down to the atmospheric level, by at least restricting the discharge flow of the fluid from the rear pressure chamber. The flow-restricting device may be a flow-inhibiting device arranged to completely inhibit the discharge flow of the fluid from the rear pressure chamber. Usually, the rear pressure chamber of the pressure-control cylinder is connected to at least one of a reservoir, the master cylinder, and a brake cylinder portion of the braking system, which portion includes the control-pressure chamber and the brake cylinder. As described below with respect to the following modes (20)-(24) of the invention, the flow-restricting device may include at least one valve arranged to restrict the discharge flow of the fluid from the rear pressure chamber to the reservoir and master cylinder. The pressure-control cylinder may or may not be arranged to deliver the fluid from the rear pressure chamber to the brake cylinder portion of the braking system. Where the pressure-control cylinder is not so arranged, the flow-restricting device need not be arranged to restrict the discharge flow of the fluid from the rear pressure chamber to the brake cylinder portion. Even where the pressure-control cylinder is arranged to deliver the fluid from the rear pressure chamber to the brake cylinder portion, the flow-restricting device need not be arranged to prevent this fluid flow, since the fluid pressure in the control-pressure chamber is higher than that in the rear pressure chamber during operation of the pressure-control cylinder, so that the fluid is not freely discharged from the rear pressure chamber to the brake cylinder portion while the pressure-control cylinder is in operation. Although the fluid pressure in the rear pressure chamber may possibly be higher than that in the control-pressure chamber in some cases, the fluid pressure in the rear pressure chamber will not be made lower than that in the control-pressure chamber as a result of the discharge flow of the fluid from the rear pressure chamber. In this sense, the flow-restricting device is not necessary to prevent the discharge flow of the fluid from the rear pressure chamber to the brake cylinder portion. However, a fluid passage connecting the rear pressure chamber and the brake cylinder portion is desirably provided with a check valve which inhibits a flow of the fluid in a direction from the brake cylinder portion toward the rear pressure chamber but permits a flow of the fluid in the reverse direction.
The above mode (19) of the invention is applicable to the braking system according to any one of the above modes (12)-(18), and the following modes of the invention are also applicable to the braking systems of the above modes (12)-(18).
(20) A braking system according to the above mode (19), further comprising a reservoir system including a reservoir which stores the fluid at a pressure substantially equal to an atmospheric level, and wherein the flow-restricting device is disposed in a fluid passage connecting the reservoir system and the rear pressure chamber, the flow-restricting device restricting the discharge flow of the fluid from the rear pressure chamber to the reservoir system at least when the fluid pressure in the brake cylinder is required to be held at the present level.
The flow-restricting device may be an electromagnetically or mechanically operated control device, like the valve device as described above with respect to the above mode (15). Where the flow-restricting device is an electromagnetic control valve, it is preferably a normally closed valve since the normally closed valve requires a smaller amount of consumption of electric power than a normally open valve, to maintain the fluid pressure in the brake cylinder. The electromagnetic control valve provided as the flow-restricting device may serve as part of the valve device described above with respect to the above mode (15).
(21) A braking system according to the above mode (19) or (20), further comprising a master cylinder system including the master cylinder, and wherein the flow-restricting device restricts the discharge flow of the fluid from the rear pressure chamber to the master cylinder system at least when the fluid pressure in the brake cylinder is required to be held at the present level.
The fluid pressure in the rear pressure chamber can be made higher than that in the master cylinder, by restricting the discharge flow of the fluid from the rear pressure chamber to the master cylinder system.
(22) A braking system according to the above mode (21), wherein the master cylinder includes a pressurizing piston which partially defines a pressurizing chamber and which is advanced by an operation of the manually operable brake operating member, to pressurize the fluid in the pressurizing chamber, and the master cylinder system further includes a stroke simulator comprising (a) a housing, (b) a simulator piston slidably received within the housing and cooperating with the housing to define a first variable-volume chamber and a second variable-volume chamber, the first variable-volume chamber being connected to the pressurizing chamber of the master cylinder, while the second variable-volume chamber being connected to the rear pressure chamber of the pressure-control cylinder, and (c)
biasing means for biasing the simulator piston in a direction that causes a volume of the first variable-volume chamber to be reduced.
(23) A braking system according to the above mode (22), wherein the flow-restricting device is disposed on at least one of upstream and downstream sides of the stroke simulator which correspond to the first and second variable-volume chambers connected to the pressurizing chamber and the rear pressure chamber, respectively.
In the braking system according to the above mode (23), the discharge flow of the fluid from the rear pressure chamber to the master cylinder system is restricted by the flow-restricting device.
(24) A braking system according to the above mode (19), wherein the flow-restricting device restricts the discharge flow of the fluid from the rear pressure chamber to a portion of the braking system other than a brake cylinder portion which includes the brake cylinder.
In the braking system according to the above mode (24), the flow-restricting device restricts the discharge flow of the fluid to the reservoir system and/or the master cylinder system, which are other than the brake cylinder portion of the braking system.
The brake cylinder portion may be a portion of the braking system which is located between the rear pressure chamber and the brake cylinder and which includes the brake cylinder, a fluid passage connecting the pressure-control cylinder and the brake cylinder, and a portion of the pressure-control cylinder which is located between the rear pressure chamber and the brake cylinder.
(25) A braking system according to any one of the above modes (19)-(24), wherein the braking-pressure control device includes a pressure-hold-requirement detecting portion operable to detect a pressure-hold requirement for holding the fluid pressure in the brake cylinder, on the basis of an operating state of the manually operable brake operating member.
While various pressure control modes of the braking system in general will be described later, there will be described a pressure-hold requirement for controlling the braking system in a pressure hold mode to hold the brake cylinder pressure at the present level. The pressure-hold requirement may be detected or obtained on the basis of at least the operating state of the brake operating member by the operator. For instance, the pressure-hold requirement is detected when the operating state of the brake operating member is held substantially constant or steady.
Alternatively, the pressure-hold requirement can be detected on the basis of both the operating state of the brake operating member and a state of an automotive vehicle equipped with the present braking system. The state of the vehicle includes a running condition, and a braking effect produced by the braking system. For instance, the pressure-hold requirement is detected when the absolute value of a difference between a desired braking effect (determined by the operating state of the brake operating member) and an actual braking effect (braking force or deceleration value of the vehicle) is smaller than a predetermined threshold value.
The vehicle running condition may be taken into account in determining whether the pressure-hold requirement is present or not. For example, the absolute value of the threshold value indicated above may be changed depending upon whether the vehicle is running or stationary. The pressure-hold requirement while the vehicle is stationary may be handled as a long-pressure-hold requirement for holding the brake cylinder pressure for a relatively long time, as distinguished from a short-pressure-hold requirement while the vehicle is running.
(26) A braking system according to any one of the above modes (19)-(25), wherein the braking-pressure control device includes an electric-energy reducing portion operable to reduce an amount of electric energy applied to the power-operated drive device after initiation of restriction of the discharge flow of the fluid from the rear pressure chamber by the flow-restricting device, as compared with an amount of electric energy applied to the power-operated drive device before the initiation of restriction.
The fluid in the rear pressure chamber is pressurized while the discharge flow from this rear pressure chamber is restricted, so that the control piston receives a drive force corresponding to the amount of electric current applied to the power-operated drive device, and a force based on the fluid pressure in the rear pressure chamber. Accordingly, the amount of electric energy required to be applied to the drive device to maintain the fluid pressure in the control-pressure chamber at a given level can be reduced, by an amount corresponding to the force based on the fluid pressure in the rear pressure chamber.
(27) A braking system according to the above mode (25) or (26), wherein the braking-pressure control device includes a surface-area-based electric-energy reducing portion operable to reduce an amount of electric energy applied to the power-operated drive device, to a value determined by an amount of electric energy required to be applied to the power-operated drive device when the pressure-hold requirement is detected by the pressure-hold-requirement detecting portion, and a ratio of an area of a front pressure-receiving surface of the control piston which partially defines the front control-pressure chamber, to an area of a rear pressure-receiving surface of the control piston which partially defines the rear pressure chamber.
(28) A braking system according to the above mode (27), wherein the area of the rear pressure-receiving surface of the control piston is smaller than that of the front pressure-receiving surface.
As described above, the amount of electric current required to be applied to the drive device to maintain the fluid pressure in the control-pressure chamber at a given level is smaller when the fluid in the rear pressure chamber is pressurized than when it is not pressurized. In this case, the amount of electric energy can be reduced to a value corresponding to a ratio S2/S1, where xe2x80x9cS1xe2x80x9d and xe2x80x9cS2xe2x80x9d represent the areas of the front control-pressure chamber and the rear pressure chamber, respectively, as described in detail in DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.
(29) A braking system according to any one of the above modes (19)-(28), wherein the braking-pressure control device includes a stroke-based electric-energy control portion operable while the discharge flow of the fluid from the rear pressure chamber is restricted by the flow-restricting device, to control an amount of electric current to be applied to the power-operated drive device, on the basis of an operating stroke of the control piston, and a control-pressure-based electric-energy control portion operable when the discharge flow is not restricted by the flow-restricting device, to control the amount of electric current, on the basis of the fluid pressure in the control-pressure chamber.
In the braking system according to the above mode (29), the amount of electric current to be applied to the power-operated drive system is controlled on the basis of the operating stroke of the control piston when the discharge flow of the fluid from the rear pressure chamber is restricted by the flow-restricting device, and is controlled on the basis of the fluid pressure in the control-pressure chamber when the discharge flow is not restricted.
If the amount of electric current were controlled on the basis of the fluid pressure in the control-pressure chamber, for instance, the fluid pressure in the control-pressure chamber would vary, resulting in a variation in the amount of electric current applied to the drive device, when the flow-restricting device is switched from its non-flow-restricting state to its flow-restricting state. This variation of the fluid pressure would cause control hunting of the amount of the electric energy. Where the operating stroke of the control piston is detected on the basis of the number of revolution of an electric motor used as the power-operated drive device, the amount of variation of the operating stroke of the control piston upon switching of the flow-restricting device is relatively small, so that the control hunting of the amount of electric current is less likely to take place.
(30) A braking system according to any one of the above modes (25)-(29), wherein the braking-pressure control device reduces an amount of electric current to be applied to the power-operated drive device, to a predetermined value, when the pressure-hold-requirement detecting portion has detected the pressure-hold requirement.
The predetermined value may be zero, or a value larger than zero. Where the flow-restricting device is arranged to completely inhibit the discharge flow of the fluid from the rear pressure chamber, the fluid pressure in the control-pressure chamber can be maintained even if the amount of electric current to be applied to the drive device is zeroed. However, the amount of electric current may be zeroed even where the flow-restricting device is not arranged to inhibit the discharge flow but to restrict it, as described later in detail in the DETAILED DESCRIPTION. While the vehicle equipped with the braking system is stationary, the amount of electric current to be applied to the drive device may be reduced to a value at which the fluid pressure in the control-pressure chamber can be maintained. In this case, it is not required to accurately control the fluid pressure in the control-pressure chamber, since the requirement is merely holding the vehicle stationary.
(31) A braking system according to any one of the above modes (25)-(30), wherein the braking-pressure control device controls an amount of electric current to be applied to the power-operated drive device, to a value determined by an operating state of the manually operable brake operating member, when the pressure-hold-requirement detecting has detected the pressure-hold requirement.
Since the fluid pressure in the control-pressure chamber is usually controlled to a value determined by the operating state of the brake operating member, it is desirable to control the amount of electric energy to be applied to the drive device, to a value determined by the operating state of the brake operating member.
(32) A braking system according to any one of claims 19-31, wherein the flow-restricting device includes an electromagnetic control valve operable in response to a signal received from the braking-pressure control device, and the braking-pressure control device includes a valve and electric-energy control portion operable to control the electromagnetic control valve and an amount of electric energy to be applied to the power-operated drive device, on the basis of an operating state of the manually operable brake operating member, while the brake cylinder is isolated from the master cylinder.
In the braking system according to the above mode (32), the fluid pressure in the control-pressure chamber is controlled to control the fluid pressure in the brake cylinder, by controlling the amount of electric current to be applied to the power-operated drive device and the electromagnetic control valve (electromagnetic flow restricting valve) on the basis of the operating state of the brake operating member while the brake cylinder is isolated from the master cylinder. The operating state of the brake operating member may be detected by a suitable detecting device, which may be arranged to detect an operating amount such as an operating force or stroke of the brake operating member, or a physical quantity which varies with the operating amount of the brake operating member. The physical quantity may be the fluid pressure in the master cylinder or the brake cylinder, a deceleration value of the vehicle equipped with the braking system, or a deceleration value of a wheel of the vehicle. The fluid pressure in the control-pressure chamber may be controlled according to the operating state of the brake operating member, a state of change of the operating state, or both of the operating state and the state of change.
For instance, the amount of electric current and the electromagnetic flow-restricting valve may be controlled such that an actual value of a physical quantity relating to the braking state (such as an actual value of the brake cylinder pressure or an actual value of the vehicle or wheel deceleration value) coincides with a desired value (desired brake cylinder pressure or desired deceleration value) which is determined by the operating state of the brake operating member.
Described more specifically, one of pressure control modes of the braking system is selected on the basis of the operating state of the brake operating member, and the power-operated drive device and the electromagnetic flow-restricting valve are controlled in the selected pressure control mode. The pressure control mode is selected on the basis of a difference between the actual and desired values of the above-indicated physical quantity, or an amount of change of the operating state of the brake operating member (amount of change of the desired value determined by the brake operating state.
Where a pressure increase mode for increasing the brake cylinder pressure is selected, the power-operated drive device is operated in the forward direction to advance the control piston, by controlling the electric energy applied to the drive device. Then, the electromagnetic flow-restricting valve is preferably placed in its non-flow-restricting state permitting the supply flow of the fluid from the reservoir system or master cylinder system into the rear pressure chamber. If the electromagnetic flow-restricting valve were placed in the non-flow-restricting state before the control piston is advanced, the fluid pressure in the rear pressure chamber would be rapidly lowered, causing a rapid drop of the fluid pressure in the control-pressure chamber.
Where a pressure hold mode for holding the brake cylinder pressure is selected, the electromagnetic flow-restricting valve is placed in its flow-restricting state for restricting the discharge flow of the fluid from the rear pressure chamber, and the amount of electric current to be applied to the drive device is reduced.
Where a pressure decrease mode for reducing the brake cylinder pressure is selected, the power-operated drive device is operated in the reverse direction to retract the control piston, by controlling the electric energy applied to the drive device. Then, the electromagnetic flow-restricting valve is placed in its non-flow-restricting state permitting the discharge flow of the fluid from the rear pressure chamber to the reservoir system or master cylinder system. In the pressure decrease mode, it is not essential to positively retract the control piston, since the control piston is retracted with a force based on the fluid pressure in the control-pressure chamber, which force is larger than the drive force produced by the drive device. The fluid pressure in the control-pressure chamber is reduced with the retracting movement of the control piston. When the pressure hold mode is followed by the pressure decrease mode, the fluid pressure in the rear pressure chamber may be reduced by utilizing the flow-restricting device. The fluid pressure in the control-pressure chamber is reduced as the fluid pressure in the rear pressure chamber is reduced by controlling the flow-restricting device.
The power-operated drive device need not be operable in the opposite directions, and may be operable in only the forward direction, since the fluid pressure in the control-pressure chamber can be reduced by reducing the drive force produced by the drive device.
The braking-pressure control device in the braking system according to the above mode (32) is preferably arranged to be operable to control the fluid pressure in the brake cylinder connected to the control-pressure chamber of the pressure-control cylinder, during a normal operation of the brake operating member.
While the flow-restricting device in the above mode (32) includes at least one electromagnetic control valve, it may include two or more electromagnetic control valves, and/or at least one mechanically operated control valve such as a check valve.
(33) A braking system according to the above mode (32), further comprising a check valve device which permits a flow of the fluid in a first direction from the rear pressure chamber toward the brake cylinder and inhibits a flow of the fluid in a second direction opposite to the first direction, and wherein the valve and electric-energy control portion includes an electric-energy increasing and reducing portion operable to first increase the above-indicated amount of electric energy and place the electromagnetic control valve in a flow-inhibiting state for inhibiting the discharge flow of the fluid from the rear pressure chamber, when the pressure-hold-requirement detecting portion has detected the pressure-hold requirement, the electric-energy increasing and reducing portion then reducing the amount of electric energy after the amount of electric energy has been once increased and the electromagnetic control valve has been placed in the flow-inhibiting state.
In the braking system according to the above mode (33), the check valve device is disposed between the rear pressure chamber and the brake cylinder, so that a flow of the fluid in the from the brake cylinder to the rear pressure chamber is prevented to prevent a drop of the fluid pressure in the brake cylinder, even when the fluid pressure in the brake cylinder is higher than that in the rear pressure chamber. When the fluid pressure in the rear pressure chamber is higher than that in the brake cylinder, on the other hand, the fluid is delivered from the rear pressure chamber to the brake cylinder.
When the amount of electric energy to be applied to the drive device is zeroed in the pressure hold mode, the control piston is retracted with the fluid pressure in the control-pressure chamber. Accordingly, the volume of the control-pressure chamber is increased with a result of reduction of its fluid pressure, and the volume of the rear pressure chamber is reduced to increase its fluid pressure. While the fluid pressure in the rear pressure chamber is lower than that in the control-pressure chamber, the pressurized fluid is not discharged from the rear pressure chamber toward the brake cylinder. When the fluid pressure in the rear pressure chamber becomes higher than that in the brake cylinder, the pressurized fluid is discharged from the rear pressure chamber toward the brake cylinder. Where the area of the front pressure-receiving surface of the control piston which partially defines the control-pressure chamber is larger than that of the rear pressure-receiving surface which partially defines the rear pressure chamber, the control piston is moved to its fully retracted position at which the fluid pressure in the rear pressure chamber is equal to that in the brake cylinder, and is kept at that level. In this case, the fluid pressure in the control-pressure chamber is lower than the level at which the pressure-hold requirement was detected, since the volume of the control-pressure chamber has been increased as a result of the retracting movement of the control piston. In view of this, the amount of electric energy is increased to increase the fluid pressure in the control-pressure chamber before the amount of electric energy is zeroed. This arrangement is effective to reduce the amount of reduction of the fluid pressure in the control-pressure chamber when the amount of electric current is zeroed. The fluid pressure in the control-pressure chamber upon zeroing of the amount of electric current can be made higher than the level upon detection of the pressure-hold requirement, if the amount of electric current has been increased to a relatively large value before zeroing of the amount of electric energy.
The amount of electric current to be applied to the drive device may be reduced to zero, or to a predetermined value larger than zero. The amount of electric current is desirably zeroed, to reduce the amount of consumption of the electric energy by the drive device.
(34) A braking system according to the above mode (33), wherein the electric-energy increasing and reducing portion includes a stroke-based electric-energy increasing portion operable to increase the amount of electric energy to be applied to the drive device, on the basis of an amount of increase of a volume of the front control-pressure chamber which takes place due to a retracting movement of the control piston.
(35) A braking system according to the above mode (33) or (34), wherein said electric-energy increasing and reducing portion includes a control-pressure-based electric-energy increasing portion operable to increase the amount of electric energy to be applied to the drive device, on the basis of an amount of reduction of a volume of the front control-pressure chamber which takes place due to a retracting movement of the control piston.
When the amount of electric current to be applied to the drive device is reduced, the control piston is retracted, and the volume of the control-pressure chamber is increased with a result of reduction of its fluid pressure. Therefore, the amount of reduction of the fluid pressure in the control pressure chamber upon reduction of the amount of electric energy can be reduced, by advancing the control piston in advance, by an amount corresponding to the amount of increase of the volume of the control-pressure chamber, that is, by an amount corresponding to the amount of reduction of the fluid pressure in the control-pressure chamber.
(36) A braking system according to any one of the above mode (33)-(35), wherein the electric-energy increasing and reducing portion includes a preset-amount increasing portion operable to increase the amount of electric energy by a predetermined amount.
Where the amount of electric energy to be applied to the power-operated drive device is increased before the amount is reduced, the amount of reduction of the control-pressure chamber upon reduction of the amount can be made smaller than where the amount is not initially increased.
(37) A braking system according to any one of the above modes (33)-(36), wherein the electric-energy increasing and reducing portion includes a holding portion operable to hold the amount of electric energy for a predetermined time after the amount of electric energy is increased and before the amount of electric energy is reduced.
When the volume of the rear pressure chamber is increased as a result of an advancing movement of the control piston, the fluid is supplied from the reservoir system or the master cylinder system into the rear pressure chamber. In this case, the amount of electric energy applied to the drive device is preferably held at the present value until the rear pressure chamber becomes fluid-tight with respect to the control-pressure chamber.
While the predetermined time may be a suitably determined constant time, or a time which varies with a distance of the advancing movement of the control piston, namely, with the amount of increase of the volume of the rear pressure chamber.
(38) A braking system according to any one of the above modes (19)-(37), wherein the flow-restricting device is a flow-inhibiting device operable to inhibit the discharge flow of the fluid from the rear pressure chamber. The flow-restricting device may include a flow-restricting valve, which may be a flow-inhibiting valve.
(39) A braking system according to any one of the above modes (19)-(37), wherein the braking-pressure control device includes:
a leakage detecting portion operable to detect an actual leakage of the fluid from the flow-restricting device or a possibility of the leakage; and
an electric-energy applying portion operable to apply the electric energy to the power-operated drive device when the leakage detecting portion has detected the actual leakage or the possibility.
The leakage detecting portion is arranged to detect an actual leakage of the fluid or a possibility of the fluid leakage. For instance, the actual leakage can be detected when the fluid pressure in the master cylinder after detection of the pressure-hold requirement is reduced by more than a predetermined amount, and the possibility of the leakage can be detected when the pressure-hold requirement is present for more than a predetermined time.
(40) A braking system according to the above mode (39), wherein the leakage detecting portion includes a portion operable to detect the actual leakage or the possibility of the leakage on the basis of at lest one of an operating state of the braking system and a running state of a vehicle equipped with the braking system.
The degree of the actual leakage of the fluid from the flow-restricting device or the possibility of the leakage can be obtained on the basis of the operating state of the braking system per se, and the amount of reduction of the brake cylinder pressure due to the fluid leakage can be obtained on the basis of the running state of the vehicle.
(41) A braking system according to the above mode (39) or (40), wherein the electric-energy applying portion controls application of the electric energy to the power-operated drive device, on the basis of at least one of an operating state of the braking system and a running state of a vehicle equipped with the braking system.
The operating state of the braking system includes the voltage and temperature of a battery provided as a power source for the power-operated drive device, a time duration of the pressure-hold requirement, and a cumulative time of the pressure-hold requirements. The battery provided to supply the power-operated drive device with an electric energy may be considered as a part of the braking system. The running state of the vehicle includes a deceleration value and a running speed of the vehicle.
On the basis of at least one of the operating state of the braking system and the running state of the vehicle, the power-operated drive device can be operated with an amount of electric energy which corresponds to the degree of the actual fluid leakage or the degree of the possibility of the fluid leakage. Accordingly, the electric-energy applying portion provided in the above mode (41) is effective to reduce the amount of reduction of the fluid pressure in the control-pressure chamber due to the fluid leakage, a minimum amount of electric energy applied to the drive device. While the vehicle is running, the electric-energy applying portion is effective to reduce the amount of reduction of the vehicle braking effect as represented by the deceleration value or rate of reduction of the running speed of the vehicle, which reduction takes place due to the fluid leakage.
(42) A braking system according to any one of the above modes (39)-(41), wherein the electric-energy applying portion determines at least one of an amount of electric energy to be applied to the power-operated drive device and a time duration for which the electric energy is applied to the power-operated drive device, on the basis of at least one of an operating state of the braking system and a running state of a vehicle equipped with the braking system.
(43) A braking system according to any one of the above modes (12)-(42), wherein the braking-pressure control device is operable in a selected one of (a) a first control state in which the fluid pressure in said brake cylinder is controlled by applying the electric current to the power-operated drive device while the brake cylinder is isolated from the master cylinder; and (b) a second control state in which said brake cylinder is held in communication with the master cylinder, for operating the brake cylinder with the pressurized fluid received from the master cylinder.
While the brake cylinder is isolated from the master cylinder, the master cylinder is preferably communication with a stroke simulator.
(44) A braking system according to any one of the above modes (12)-(43), further comprising a stroke simulator and a simulator-switching device, and wherein the stroke simulator includes (a) a housing, (b) a simulator piston slidably received within the housing and cooperating with the housing to define a first variable-volume chamber and a second variable-volume chamber, the first variable-volume chamber being connected to a pressurizing chamber of the master cylinder, while the second variable-volume chamber being connected to the rear pressure chamber of the pressure-control cylinder, and (c) biasing means for biasing the simulator piston in a direction that causes a volume of the first variable-volume chamber to be reduced,
and wherein the simulator-switching device is operable to switch the stroke simulator between an operable state which permits a change of a volume of the first variable-volume chamber according to the operation of the manually operable brake operating member, and an inoperable state which inhibits the change of the volume of the first variable-volume chamber.
The simulator-switching device may be arranged to permit and inhibit the change of the volume of the first variable-volume chamber or the second variable-volume chamber. The simulator-switching device may be disposed upstream or downstream of the stroke simulator (on the side of the first variable-volume chamber or the second variable-volume chamber). The simulator-switching device may be a device operable to isolate the second variable-volume chamber from a low-pressure source such as a reservoir. In the braking system according to the above mode (43), the stroke simulator is preferably placed in the operable state when the braking-pressure control device is in the first state, and in the inoperable state when the braking-pressure control device is in the second state. Further, the flow-restricting device described above may function as the simulator-switching device.
(45) A braking system according to any one of the above modes (12)-(44), further comprising a check valve device which permits a flow of the fluid in a first direction from the rear pressure chamber toward the brake cylinder and inhibits a flow of the fluid in a second direction opposite to the first direction.
In a normal operation of the braking system, the braking-pressure control device is placed in the first state in which the fluid pressure in the brake cylinder is controlled by controlling the pressure-control cylinder. In this first state, the fluid pressure in the brake cylinder is higher than that in the rear pressure chamber. However, the discharge flow of the fluid from the brake cylinder to the rear pressure chamber is inhibited by the check valve device, to prevent reduction of the fluid pressure in the brake cylinder. On the other hand, a defect of the flow-restricting device or a failure of the electric system of the braking system may prevent a discharge flow of the fluid from the rear pressure chamber, causing the fluid to be kept within the rear pressure chamber. In this case, the brake cylinder is communicated with the master cylinder, and the fluid is discharged from the rear pressure chamber to the brake cylinder through the check valve device when the fluid pressure in the brake cylinder is lowered upon releasing of the brake operating member. Thus, the fluid can be returned to the master cylinder, so that the master cylinder is returned to its original position in which the pressurizing chamber is filled with the fluid.
The check valve device may be provided in a braking system which does not include the flow-restricting device. In this case, too, the check valve device permits the fluid to be discharged from the rear pressure chamber and returned to the master cylinder.
(47) A braking system characterized by comprising:
a hydraulically operated brake cylinder for operating a brake;
a master cylinder including a pressurizing piston which partially defines a pressurizing chamber and which is operable according to an operation of a manually operable brake operating member, to pressurize a working fluid in the pressurizing chamber;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front pressure-control chamber being connected to the brake cylinder;
a stroke simulator includes (a) a housing, (b) a simulator piston slidably received within the housing and cooperating with the housing to define a first variable-volume chamber and a second variable-volume chamber, the first variable-volume chamber being connected to the pressurizing chamber of the master cylinder, while the second variable-volume chamber being connected to the rear pressure chamber of the pressure-control cylinder, and (c) biasing means for biasing the simulator piston in a direction that causes a volume of the first variable-volume chamber to be reduced; and
a braking-pressure control device operable in a selected one of (i) a first control state in which the fluid pressure in the brake cylinder is controlled by applying an electric current to the power-operated drive device while the brake cylinder is isolated from the master cylinder and while the stroke simulator is placed in an operable state which permits a change of a volume of the first variable-volume chamber according to the operation of the manually operable brake operating member; and (ii) a second control state in which the brake cylinder is held in communication with the master cylinder, while permitting a flow of the fluid from the rear pressure chamber to the second variable-volume chamber.
In the braking system according to the above mode (46), the braking-pressure control device is operated in the second control state upon releasing of the brake operating member. In this second control state, the brake cylinder is communicated with the master cylinder, and the fluid is permitted to be discharged from the rear pressure chamber to the second variable-volume chamber of the stroke simulator, so that the fluid is returned from the first variable-volume chamber to the master cylinder as the fluid is returned from the rear pressure chamber to the second variable-volume chamber.
The technical feature according to any one of the above modes (12)-(45) is applicable to the braking system according to the above mode (46).
(47) A braking system comprising:
a hydraulically operated brake cylinder for operating a brake;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front pressure-control chamber being connected to the brake cylinder;
a braking-pressure control device operable to control application of an electric energy to the power-operated drive device, to control a pressure of a working fluid in the brake cylinder; and
a flow-restricting device operable to restrict a discharge flow of the fluid from the rear pressure chamber when a predetermined condition is satisfied.
The predetermined condition may be satisfied when the brake cylinder pressure is required to be held at the present level, when the braking system becomes defective, or when a vehicle equipped with the braking system is stationary.
The flow-restricting device preferably includes at least one electromagnetic control valve. The electromagnetic control valve may be switched to a flow-restricting state when the predetermined condition is satisfied.
The technical feature according to any one of the above modes (12)-(46) is applicable to the braking system according to the above mode (47).
(48) A braking system comprising:
a hydraulically operated brake cylinder for operating a brake;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front pressure-control chamber being connected to the brake cylinder;
a braking-pressure control device operable to control application of an electric energy to the power-operated drive device, to control a pressure of a working fluid in the brake cylinder; and
a flow-restricting device operable to restrict a discharge flow of the fluid from the rear pressure chamber when the pressure of the fluid in the brake cylinder is required to be held at a present level.
The technical feature according to any one of the above modes (12)-(47) is applicable to the braking system according to the above mode (48).
(49) A braking system comprising:
a hydraulically operated brake cylinder for operating a brake;
a master cylinder including a pressurizing piston which partially defines a pressurizing chamber and which is operable according to an operation of a manually operable brake operating member (34), to pressurize a working fluid;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front pressure-control chamber being connected to the brake cylinder;
a fluid passage connecting the rear pressure chamber and the pressurizing chamber of the master cylinder;
a stroke simulator disposed in the fluid passage and includes (a) a housing, (b) a simulator piston slidably received within the housing and cooperating with the housing to define a first variable-volume chamber and a second variable-volume chamber, the first variable-volume chamber being connected to the pressurizing chamber of the master cylinder, while the second variable-volume chamber being connected to the rear pressure chamber of the pressure-control cylinder, and (c) biasing means for biasing the simulator piston in a direction that causes a volume of the first variable-volume chamber to be reduced; and
a braking-pressure control device operable to control an electric energy to be applied to the power-operated drive device, for controlling the pressure of the fluid in the front control-pressure chamber, to thereby control the pressure in the brake cylinder.
The technical feature according to any one of the above modes (12)-(48) is applicable to the braking system according to the above mode (49).
(50) A braking system comprising:
a hydraulically operated brake cylinder for operating a brake;
a master cylinder including a pressurizing piston which partially defines a pressurizing chamber and which is operable according to an operation of a manually operable brake operating member, to pressurize a working fluid;
a power-operated drive device;
a pressure-control cylinder having a control piston which is operable by the power-operated drive device and which partially defines a front control-pressure chamber and a rear pressure chamber on respective front and rear sides thereof, the front pressure-control chamber being connected to the brake cylinder;
a master-cylinder passage connecting the rear pressure chamber and the pressurizing chamber of the master cylinder;
a reservoir which stores the working fluid under a pressure substantially equal to an atmospheric level;
a reservoir passage connecting the rear pressure chamber and the reservoir; and
a braking-pressure control device operable to control application of an electric energy to the power-operated drive device, to control a pressure of a working fluid in the brake cylinder.
The technical feature according to any one of the above modes (12)-(49) is applicable to the braking system according to the above mode (50).
(51) A braking system according to the above mode (50), wherein the master-cylinder passage is provided with a stroke simulator and a simulator control valve which are connected in series with each other.
The simulator control valve may be an electromagnetic shut-off valve which is opened and closed by energization and de-energization of its coil, or a linear control valve the opening of which is variable with an amount of electric current applied to its coil. The simulator control valve may be disposed between the stroke simulator and the master cylinder, or between the stroke simulator and the rear pressure chamber of the pressure-control cylinder.
A check valve may be disposed in parallel connection with the stroke simulator, such that the check valve permits a flow of the fluid in a direction from the rear pressure chamber toward the master cylinder and inhibits a flow of the fluid in the reverse direction. The check valve permits the fluid to be rapidly returned from the rear pressure chamber to the master cylinder.
(52) A braking system according to the above mode (50), wherein the master-cylinder passage is provided with a stroke simulator and a check valve which are connected in series with each other such that the check valve is disposed between the stroke simulator and the rear pressure chamber.
The check valve in the above mode (52) is arranged to permit a flow of the fluid in a direction from the stroke simulator toward the rear pressure chamber and inhibit a flow of the fluid in the reverse direction.
(53) A braking system according to the above mode (50) or (52), wherein the reservoir passage is provided with at least one of (a) a reservoir communication valve which is operable switched at least between an open state and a closed state, and (b) a check valve which permits a flow of the fluid in a first direction from the reservoir toward the rear pressure chamber and inhibits a flow of the fluid in a second direction opposite to the first direction.
Since the check valve in the above mode (53) permits the fluid flow from the reservoir into the rear pressure chamber as the volume of the rear pressure chamber is increased, an advancing movement of the control piston is permitted so that the fluid pressure in the rear pressure chamber is prevented from being lowered below the atmospheric level.
Where the reservoir communication valve and the check valve are disposed in parallel connection with each other, the control piston can be advanced even while the reservoir communication valve is in the closed state. The reservoir communication valve and the check vale may function as the valve device described above with respect to the above mode (15).
(54) A braking system according to the above mode (51) or (52), wherein the reservoir passage is connected to a portion of the master-cylinder passage between the simulator control valve and the stroke simulator.
In the braking system according to the above mode (54), the simulator control valve is disposed between the stroke simulator and the rear pressure chamber, and the reservoir passage is connected to a portion of the master-cylinder passage between the simulator control vale and the stroke simulator. When the simulator control valve is placed in the closed state, this simulator control valve inhibits flows of the fluid from the rear pressure chamber to both the stroke simulator and the reservoir. In this case, the stroke simulator may be placed in its operable state while the reservoir communication valve is held in the open state and while the rear pressure chamber is isolated from the stroke simulator. Thus, the operable state of the stroke simulator can be established while at the same time the discharge flow of the fluid from the rear pressure chamber can be inhibited by the simulator control valve.
(55) A braking system according to the above mode (54), wherein the portion of the master-cylinder passage is connected by a connecting passage to the front control-pressure chamber, and the connecting passage is provided with a check valve which permits a flow of the fluid in a first direction from the portion toward the rear pressure chamber and inhibits a flow of the fluid in a second direction opposite to the first direction.
In the braking system according to the above mode (55), the fluid can be delivered from the rear pressure chamber to the control-pressure chamber while the simulator control valve also functioning as a flow-inhibiting valve is placed in the open state. Further, the fluid can be returned from the rear pressure chamber to the master cylinder through the simulator control valve placed in the open state when the brake operating member is released. The connecting passage, check valve and the flow-inhibiting valve (simulator control valve) may be considered to constitute a check valve device. The flow-inhibiting valve is preferably a normally open valve.
(56) A braking system according to the above mode (52), wherein the reservoir passage is provided with a reservoir communication valve, and a portion of the reservoir passage between the reservoir communication valve and the reservoir is connected by a connecting passage to a portion of the master-cylinder passage between the stroke simulator and the check valve, the connecting passage being provided with a check valve.
The check valve disposed in the connecting passage provided in the above mode (56) may be arranged to permits a flow of the fluid in a direction from the reservoir passage toward the master cylinder passage, and inhibit a flow of the fluid in the reverse direction. In the braking system according to the above mode (56), the stroke simulator can be placed in its operable state even where the reservoir communication valve is placed in the closed state, as described in the DETAILED DESCRIPTION. When the reservoir communication valve is in the closed state, this valve and the check valve provided in the master-cylinder passage inhibit the discharge flows of the fluid from the rear pressure chamber to the reservoir and the stroke simulator, respectively.